Compared to a conventional trench metal oxide semiconductor field effect transistor (hereinafter MOSFET), a shielded gate trench MOSFET is more attractive due to its reduced Cgd (capacitance between gate and drain) in accordance with reduced Qgd (charge between gate and drain), and increased breakdown voltage of the trench MOSFET, making an excellent choice for power switching applications such as inverter and DC to DC power supply circuits. However, for those power switching applications, MOSFET body diode reverse recovery charge is very important due to the fact that high body diode reverse recovery charge value increase complimentary MOSFET turn-on loss, which pronounces especially when the shielded gate trench MOSFET is used for the low-side switch.
FIG. 1A shows a shielded gate trench MOSFET 100 disclosed in prior art U.S. Pat. No. 7,768,064 comprising a resistive element 101 between shielded electrode 102 and source metal for reduction of the reverse recovery charge of a parasitic body diode in the shielded gate trench MOSFET 100. Besides, the shielded gate trench MOSFET 100 further comprises: a planar source-body contact to contact n+ source region 103 and P body region 104 with the source metal 105; and a p+ ohmic body contact doped region 106 to reduce the contact resistance between the source metal 105 and the P body region 104.
From FIG. 1B which is a top view of the shielded gate trench MOSFET 100, it can be seen that, the resistive element 101 (illustrated by dash lines) is placed between end contacts 106 and 107, wherein the end contact 106 is connected to the shielded electrode 102 (as shown in FIG. 1A) while the end contact 107 is connected to the source metal 105. However, according to the prior art, the resistive element 101 is implemented by poly-silicon, diffusion or other suitable material as long as the resistive element 101 is greater than overall distribution or spreading resistance of the shielded electrode 102, therefore, the implementation of the resistive element 101 will need additional cost such as additional mask for poly-silicon resistor. Moreover, if the resistive element 101 is made of diffusion such as n+ source, an additional parasitic bipolar will be introduced degrading in the breakdown voltage.
Furthermore, the shielded gate trench MOSFET 100 used planar source-body contacts as shown in FIG. 1A, resulting in difficulty for cell pitch shrinkage.
Accordingly, it would be desirable to provide a new and improved power semiconductor device, for example a shielded gate trench MOSFET having high switching speed and high cell density without requirement of additional cost.